The invention relates to a pump jack for use in pumping liquids, and more specifically to a pump jack for pumping oil from ground wells. The invention also relates to utilizing resources available at the well head to provide the energy, and motive power required to operate a pump jack.
Conventional pump jacks for pumping various liquids generally comprise a rocker arm pivotally mounted intermediate its ends on a main support member. On one limb (hereinafter referred to as the sucker-rocker limb) of this rocker arm the sucker rods are attached by flexible means to a typical "horsehead" and assembly specifically designed to maintain the sucker rods in vertical alignment within the well. The sucker rods which descend into the well are connected to the piston and pump which are mounted within the well near the bottom or at the level at which the liquid to be pumped is located. Usually, a counterweight is mounted on the opposed limb of the rocker arm (hereinafter referred to as the drive limb) to counter balance the greater weight of the sucker rod and piston assembly. To pivot the rocker arm and thus to reciprocate the sucker rods vertically within the well, the upper end of a motor driven mechanism is mounted fixedly to the drive limb of the rocker arm. Such a motor assembly is usually of the rotary type, and the rotation of a drive shaft mounted to a motor causes the sucker rod to reciprocate in a vertical direction as measured by the motion at the horsehead. Such a motor is either electrical or gasoline driven, in either case requiring attention to the provision of a source of energy either providing gasoline or other burnable hydrocarbon or the running of electrical wires to what is potentially a remote location.
An additional problem that is involved with such a motor driven type of pump jack is that the rotary motion of a motor be it electrical or gasoline driven is at considerably higher shaft speed than the desired speed at which the horsehead is intended to be reciprocated. Therefore, reducing speed, principally by gear reduction or other lever arm type reduction mechanism, and controlling of the speed itself by governors on the motor constitute built-in mechanical inefficiency since the efficiency of such gear reduction and multiple lever connections removes some of the energy available for driving the pump jack in the appropriate reciprocating manner.
In order to correctly operate such a rocker arm type of pump jack a counter weight is mounted on the drive limb of the rocker arm as was mentioned above. The purpose of a counter weight is to offset the considerably larger weight of the piston sucker rods and also of the column of oil residing above the piston which is being lifted by the motion of the pump jack. Such counterweighting systems can be of the over counterweighted or under counterweighted type. An over counterweighted system is one in which the counterweight more than compensates for the weight of the oil, the piston, the sucker rods, and the horsehead in addition to the weight of the sucker rod limb of the rocker arm such that when all power is removed from the system the counterweight will pull the piston to its uppermost position within the well. In such a system the force on the drive limb of the rocker arm tends to push the counterweighted drive limb in an upward direction while pushing the sucker-rod limb with horsehead downward. Simple removal of power will allow the counterweight to lift the column of oil and the piston. It should be noted that on over counterweighted system is an unusual design. The under counterweighted system which is considerably more typical has a counterweight that less than compensates for the above weights on the sucker-rod limb, therefore, when power is removed the horsehead tends to move to a downward position with the counterweight high in the air.
A significant problem in the operation of oil pump jacks is that they tend to be located in remote areas and also tend not to be too close together thereby making the provision of power to operate the pump jacks somewhat of a problem. As was mentioned above, the typical pump motor is either a gasoline engine driven or electrically-driven motor. An electrically-driven motor can be operated by stringing power lines to each of the wells no matter how remote or by local storage batteries which would have to be recharged or renewed on a periodic basis. A gasoline engine requires the provision of gasoline to storage tanks immediately adjacent the engine on a periodic basis in order to maintain the power source. Oil directly from the well cannot generally be burned in a gasoline engine because of the many high burning hydrocarbons that will tend to plug manifolds and carburetors.
The use of the natural gas which is available in most wells in the midwest and in the southwest of the United States has been limited to high gas production wells which are utilized in interstate or intrastate gas pipelines. If quantities of gas are not available in sufficient quantities to make it practical to pipe to such pipelines such gas is merely vented to the atmosphere. In the state of Ohio, such gas is often simply vented to the atmosphere because there is no economic gain from utilizing such small quantities over the vast distances of piping that would be necessary in order to connect to main intrastate or interstate gas lines and the proximity of many gas wells in Ohio or oil wells with some gas production to mountainous areas of the state additionally add to the problems and cost of laying such pipelines for small quantities of gas.